1. FIELD OF THE INVENTION
This invention relates to a disposable safety syringe, such as a dental syringe, having a pre-filled fluid medication cartridge and a double-ended hypodermic needle cannula, and, more particularly, to means by which the needle cannula may be relocated from an axially extended position, at which to inject the fluid contents of the medication cartridge into a targeted tissue area, to a retracted position, at which the cannula is withdrawn into and completely shielded by the medication cartridge at the interior of the syringe cylinder.
2. PRIOR ART
Dental syringes of the type having a pre-filled cartridge of fluid medication and a double-ended hypodermic needle are well-known in the art for injecting such medication from the cartridge to a targeted tissue area of a patient. However, at the completion of the injection, the needle is typically locked in an axially extended position projecting outwardly from a distal bore formed through the syringe cylinder.
In some cases, the syringe may be used to treat a patient having a communicable disease. Prior to disposing the syringe, the hypodermic needle is frequently broken or destroyed to prevent reuse. Dental office workers are especially susceptable to accidental and potentially infectious needle strikes due to the careless handling or breaking of the needle and disposing of the syringe after use. The resulting mini-accident caused by an accidental needle strike typically requires a blood test for such diseases as AIDS and hepatitis. The corresponding cost and ineffiency of testing dental office workers who have received such an accidental needle strike result in considerable waste, which may be particularly damaging to a dental facility which is striving for economy.
The following patent applications, which are assigned or will be assigned to the assignee of the present patent application, disclose syringes having a pre-filled medication cartridge and a needle which is retractable within the syringe cylinder:
Application Ser. No. 39,715 filed Apr. 20, 1987 and entitled "Dental syringe having an automatically retractable needle"; application Ser. No. 101,251 filed Sept. 25, 1987 and entitled "Disposable, presterilizable syringe for a pre-filled medication cartridge"; and Application Docket No. HMTC-34 entitled "Retractable needle syringe with integral spring".